Lead(II)-Based Coordination Polymer Exhibiting Reversible Color Switching and Selective CO2 Photoreduction Properties.

Herein, we report a new photofunctional Pb-S-based coordination polymer (CP) with the formula [Pb(ATAT)(OAc)]n (ATAT = 3-amino-5-mercapto-1,2,4-triazole, OAc = acetate, CP1). Apart from its photoactive one-dimensional (1D) (-Pb-S-)n chain, CP1 is also composed of another 1D (-Pb-O-)n chain that originates from the coordination with acetate. The coordinated acetate can be exchanged with water (H2O) or dimethyl sulfoxide (DMSO), leading to the formation of a CP1-H2O or CP1-DMSO structure that exhibits a distinct change in optical properties, including a white-to-yellow color change. The structural transformation of CP1 to CP1-H2O and CP1-DMSO, and its subsequent recovery to the original CP1 structure could be controlled by the presence or absence of acetic acid vapor; the transformation was completely reversible. CP1 absorbed light with wavelengths shorter than 390 nm, with an estimated bandgap of 3.18 eV. Density functional theory calculations indicated that the valence band of CP1 is mainly formed by N and S orbitals originating from the ATAT unit, whereas the conduction band is composed of the Pb orbitals. Even without any modification, such as the incorporation of a molecular catalyst, CP1 reduced CO2 into formate under UV light with >99% selectivity.

Tin(II)-Based Metal-Organic Frameworks Enabling Efficient, Selective Reduction of CO2 to Formate under Visible Light.

Certain metal complexes are known as high-performance CO2 reduction photocatalysts driven by visible light. However, most of them rely on rare, precious metals as principal components, and integrating the functions of light absorption and catalysis into a single molecular unit based on abundant metals remains a challenge. Metal-organic frameworks (MOFs), which can be regarded as intermediate compounds between molecules and inorganic solids, are potential platforms for the construction of a simple photocatalytic system composed only of Earth-abundant nontoxic elements. In this work, we report that a tin-based MOF enables the conversion of CO2 into formic acid with a record high apparent quantum yield (9.8 % at 400 nm) and >99 % selectivity without the need for any additional photosensitizer or catalyst. This work highlights a new MOF with strong potential for photocatalytic CO2 reduction driven by solar energy.